Suction Cup Tricks

It was the third practice ILS approach of the day. My instrument student had been doing well turning onto the localizer, adjusting for any crosswind component, and intercepting the glideslope. But as soon as he passed the outer marker, things began to go down hill. He began making wild S-turns across the localizer. He was jockeying the power and elevator, and the nose was oscillating above and below the horizon like a theme-park ride. He ultimately pegged the needles, forcing a missed approach.

Obviously the student had been chasing the localizer and glideslope needles, and overcorrecting for any deviations. In a nutshell, his approaches were not stabilized. Despite my harping against needle-chasing, it wasn't sinking in.

On this last approach of the day, I remembered a trick that my instrument instructor had used on me many years ago. You see, I had experienced this same problem - in spades. As we approached the outer marker, I reached in my pocket, pulled out an instrument cover, and popped it on the face of the CDI. Even though my student was under the hood I could sense that he was pondering how he was going to complete the approach with no localizer or glideslope information.

"Trust me," I said. "Concentrate on the DG, VSI, and airspeed." I urged him to continue flying the heading that had been working since he intercepted the localizer, and to set his pitch for a descent rate of 500 feet per minute at an airspeed of 95 knots. I instructed him to set the power to a level that would give him the required descent rate and airspeed and then leave it alone.

In one of my more humane gestures, I removed the suction cup for a short moment every 30 seconds to confirm the accuracy of the approach. Miraculously, this time the needles were centered within one dot all the way to decision height. The light had finally come on for him.

When you use this technique, remind your student that as you descend on the approach, the crosswind component will probably decrease. When you momentarily remove the suction cup, this change will be indicated by the aircraft's being slightly off the localizer. The student can make the small heading correction needed to compensate for the changing wind, but must return to concentrating on flying the new heading as the CDI is once again covered.

I found that an airspeed of 90 knots and a descent rate of 500 feet per minute works well for a Cessna 172, but these numbers will have to be adjusted for other types of aircraft. All instrument pilots should determine the appropriate pitch, power settings, and airspeeds for their own aircraft for precision and nonprecision approaches, holding patterns, and other flight regimes so that in hard IFR one is not scrambling to find the right combination.

Richard Hiner is vice president of training for the AOPA Air Safety Foundation. He has been an active flight instructor for 18 years.